How to test for minimum amount of items in inventory and execute a command if true

I am using the AmazingKit plugin on my Minecraft server to make inventory kits for players. In a command block I have the following command:
/tellraw @p ["",{"text":"Iron","clickEvent":{"action":"run_command","value":"_____"}},{"text":" / "},{"text":"Gold","clickEvent":{"action":"run_command","value":"_____"}}]
Which prints the following result: Iron / Gold
.
When a player clicks on Iron, what command should I write where the empty space is _____ in order to check if the player has at least (>=) 20 iron ingots in his inventory and if he/she does, remove 20 iron ingots and execute /kit Basic
. If the player has less than 20 iron ingots in inventory, the command won't be executed. Instead, Insufficient amount of iron ingots will be printed out.
Same applies when a player clicks on "Gold".
I'm on 1.14 version
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How do you test inventory items?
You can use the /invsee <name> command to achieve this. You can also modify a users inventory using this command.What is the command to check inventory?
How to Enter the CommandMinecraft Bedrock - Test For Items In Inventory (Mobile/Xbox/PS4/Windows 10/Switch)
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